Phosphate flotation process



United States Patent 3,482,688 PHOSPHATE FLOTATION PROCESS Charles H. G. Bushell, Montrose, British Cloumbia, and

Horst E. Hirsch, Trail, British Columbia, Canada, assignors to Cominco Ltd., Montreal, Quebec, Canada, a corporation of Canada No Drawing. Filed Julyv 8, 1966, Ser. No. 563,662 Int. Cl. B03d N02 US. Cl. 209-166 5 Claims ABSTRACT OF THE DISCLOSURE A process for beneficiating phosphate rocks high in silicates and calcium and magnesium carbonates comprising subjecting said materials in comminuted form to an anionic froth flotation in an aqueous solution of a soluble fluoride selected from the group consisting of ammonium, hydrogen, sodium and potassium fluoride in the presence of a fatty acid collector. The resulting products are a froth product containing magnesium and calcium carbonates and a phosphate-enriched underflow concentration product.

This invention relates to a process for the beneficiation of phosphate-bearing materials and is particularly directed to a flotation process for the concentration of phosphate minerals such as apatite in phosphate rock.

Phosphate rock used in the production of phosphoric acid and phosphate fertilizers has phosphate minerals which occur in a plurality of forms, the more common of which and most important commercially being apatite, Ca (PO F, found normally in association with gangue minerals such as silicates, calcite, dolomite and magnesite. The silicate or silica constituent of the rock commonly is removed by subjecting the comminuted rock to a primary anionic flotation wherein the phosphate minerals are collected and concentrated as a forth product and the silica minerals depressed and removed in the underflow as tailings. The froth product may then be subjected to a cationic flotation wherein the residual silica in the primary froth product is collected in the second stage froth as failings and the valuable phosphate minerals depressed and removed in the underflow as a concentrate product. The calcite, magnesite and dolomite in their respective forms as calcium and magnesium carbonates have flotation characteristics similar to that of the phosphate minerals resulting in the concentration of the carbonates with the phosphate minerals.

In that carbonates present in the phosphate concentrate preferentially react with sulphuric acid when the concentrate is used in the wet phosphoric acid process for the production of phosphoric acid, the carbonates present cause undesirable foaming in the reactor chambers with resulting interruptiton of the operation and undue consumption of the acids. Also, the magnesium present in the phosphate concentrate forms soluble salts which increase the viscosity of phosphoric acid, and cause other difficulties when the acid is ammoniated to produce ammonium phosphate fertilizers.

It is also known to use soluble alkaline phosphates at a pH between 6 and 7 in an anionic flotation system to separate calcium carbonate from phosphate minerals whereby the calcium carbonate is collected as tailing in the froth and the phosphate minerals are depressed and concentrated as product in the underflow. For example, United States Patent No. 3,113,838 issued Dec. 10, 1963, discloses a process wherein sulphuric acid is employed to attack a portion of the phosphate minerals in an ore to produce phosphoric acid for transformation of the calcium phosphate into a soluble phosphate. This practice has been found unsatisfactory in that excessive quantities of sulphuric acid are consumed by preferential reaction with the carbonates rather than the phosphates and, as a result of the acid attack, the characteristics of he ore are altered. Also, the silica and silicate minerals report with the phosphate minerals interfering with the subsequent operation of the Wet phosphoric acid process.

We have found that the bulk of the magnesium and calcium carbonates can be removed from phosphatebearing materials by anionic froth flotation of the comminuted material suspended in an aqueous solution of a soluble fluoride selected from the group consitsing of ammonium, hydrogen, sodium and potassium fluorides in the presence of a fatty acid collector. The resulting products are a froth product containing magnesium and calcium carbonates and a P O -enriched underflow concentrate product.

It is an important object of the present invention, therefore, to provide a method of beneficiating comminuted phosphate rocks high in silicates and calcium and magnesium carbonates to produce a concentrate rich in phosphate minerals and relatively low in calcium and magnesium carbonates and silicate gangue minerals.

It is another object of the present invention to provide a method of beneficiating phosphate rocks and concentrates of hard rock phosphates known as apatite and collophane, by anionic flotation.

These and other objects of the present invention and the manner in which they can be attained will become apparent from the following detailed description of the embodiments and examples of the process.

According to the process of the invention, the phosphate rock to be beneficiated preferably is subjected, after appropriate comminutiou, to a primary anionic flotation using fatty acid collector reagents such as oleic acid, stearic acid, tall oils and the like to provide an enriched phosphate concentrate containing calcium and magnesium carbonates as a froth product and a silica tail as an underflow depressed product.

The phosphate-enriched froth concentrate is then subjected to an anionic flotation in an aqueous solution of a soluble fluoride present in amount of from about 1 to about 10 g.p.l., said solution having a pH within the range of from about 4.5 to about 7, preferably within the range of 5.8 to 6. The soluble fluoride can be selected from the group consisting of ammonium, hydrogen, sodium and potassium fluorides. The pH control can be maintained by the introduction to the solution of, for example, hydrofluoric acid, ammonium hydroxide and ammonia. The anionic collector may be a fatty acid selected from the group consisting of oleic acid, stearic acid, tall oil and the like.

The following examples show the effectiveness of the present process in the treatment of a collophane rock concentrate, collophane being a microor crypto-crystalline form of apatite. These examples are furnished for purposes of illustration only and it will be understood that the examples will not be construed as placing any limitations on the scope of the invention than as appears in the appended claims.

EXAMPLE 1 In this example of the process of our invention a primary phosphate concentrate feed containing 30.3% P 0 45.5% CaO, 0.9% MgO and 10.6% SiO and ground to pass mesh was suspended in an aqueous solution containing 5.0 g.p.l. of ammonium acid fluoride (NH F-HF). The suspension was adjusted to contain approximately 30 to 35% solids and the pH adjusted to 5.8-6.0 using NH OH or HP as required. The suspension was then subjected to flotation using a fatty acid flotation reagent.

Table I below gives the results of this test:

TABLE I.DEPOR'IMENT OF (3210, MgO, P205 AND SiOz Assays, percent Distribution, percent (aceum. floats) NHJXHF Fatty Acid in pulp, lbjton g.p.l plI (accumul) P105 CaO MgO SiO1 IL* Wt. P205 CaO MgO S102 IL *IL means Ignition Loss and is a measure of the CO2 plus other volatile constituents, notably H2O.

In this example the float products 1, 2 and 3 account for 10.8% by Weight of the feed and collectively account for 70% of the original MgO together with smaller amounts of CaO and S102. The concentrates, shown as the underflow, account for 89.2% by weight of the feed and contain 31.4% P 0 45.8% CaO, 0.3% MgO and 11.0% SiO EXAMPLE 2 phate-bearing material in an aqueous solution of a soluble fluoride selected from the group consisting of ammonium, hydrogen, sodium and potassium fluorides, adjusting the pH of said aqueous solution within the range of from about 4.5 to about 7, adding a flotation collector for the calcium and magnesium carbonate minerals, subjecting the mixture to froth flotation, and withdrawing an overflow product containing said carbonate minerals and an underflow product comprising a P O -enriched concentrate.

2. In a process as claimed in claim 1, said soluble fluoride having a concentration in said aqueous solution of at least 1 g.p.l.

3. In a process as claimed in claim 1, said soluble fluoride having a concentration in said aqueous solution within the range of from about 1 g.p.l. to about 10 g.p.l.

4. In a process as claimed in claim 3, adjusting the pH N NaF PULPS NaF Distribution, percent in Fatty Acid Assays, percent (aceum. floats) pulp, pH 1b.]ton Float N o g.p.l. pH modifier (accumuL) P20 MgO IL Wt. P105 MgO IL 1 25. 5 3. 5 12. 0 3. 7 3. 2 16. 3 l). 7 2 12. 8 8. 5 27. 1 7. 1 4. 6 52. 2 28. 2 3 22. 2 3. O 12. 8 14. 1 O. 8 7S. 5 46. 3 Underflow 31. 5 0. 2 3. 1 85. 0 90. 2 21. 5 53. 7 Feed 30. 0 0. 8 5. O 100 100 100 100 *IL means Ignition Loss and is a measure of the CO2 plus other volatile constituents,

notably H2O.

IN NaF PULPS NaF Distribution, percent in Fatty Acid Assays, percent (aceum. floats) pulp, pH lb./ton

Float No. g.p.l pH modifier (accumuL) P205 MgO IL Wt. P205 MgO IL* 1 2. 0 5. 8-6. 0 HF 0. 84 19. 4 7. 0 19. 7 3. 4 2. 2 27. 2 12. 7 6. 0 20. 8 8. 1 4. 9 60. O 31. 5

*IL means Ignition Loss and is a measure of the CO2 plus notably H20.

In Table I1(a) 78.5% by weight of the MgO contained in the original feed was rejected in the float, and in Table 11(b), 70.1% of the MgO was rejected.

The present invention provides a number of important advantages. Siliceous phosphate rock can be beneficiated with a low consumption of additives and eflicient removal of carbonates, especially magnesium containing carbonates. Phosphoric acid having a low magnesium salt content and suitable for the production of high quality phos phate fertilizers can be produced from this phosphate concentrate.

What we claim as new and desire to protect by Letters Patent of the United States is:

1. A process for beneficiating phosphate-bearing material containing apatite and calcium and magnesium carbonates comminuted for the substantial liberation of phosphate minerals from calcium and magnesium carbonate minerals and concentrated as a froth product by primary other volatile constituents,

of said aqueous solution within the range of from about 5 .8 to about 6.

5. A process for producing a phosphate concentrate relatively low in magnesium content from phosphate bearing materials containing calcium and magnesium carbonates and silica which comprises the steps of subjecting said phosphate bearing material in finely divided form to a primary anionic flotation operation, separately withdrawing from said primary flotation operation an underflow tailings product high in silica content and a phosphate enriched float product containing calcium and magnesium carbonates, suspending said phosphate enriched float product in an aqueous solution of a soluble fluoride selected from the group consisting of ammonium, hydrogen, sodium and potassium fluorides, adding to the resultant suspension a fatty acid flotation reagent, subjecting the suspension to a secondary anionic flotation operation, and withdrawing from said secondary flotation operation 6 an overflow product relatively high in calcium and mag- 3,361,257 1/ 1968 Maseman 209166 nesium carbonate content and an underfiow product com- 2,442,455 6/ 1948 Booth 209166 prising a phosphate concentrate relatively low in mag- 3,259,242 7/1966 Snow 209166 nesium content. FOREIGN PATENTS References Cited UNITED STATES PATENTS 5 9/1950 Keck B. Prlmary EXammer 3,113,838 12/ 1963 Perri 209-166 X ROBERT HALPER, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,482,688 December 9, 1969 Charles H. G. Bushell et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 61 and column 5, lines 3 and 4, "magnesium" should read calcium and magnesium carbonate Signed and sealed this 29th day of December 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

